Curiosity’s photos may show evidence of ancient life on Mars

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A new paper in the journal Astrobiology is raising eyebrows, as it argues that recent photos of the Martian surface show strong evidence of ancient life. Though it’s only a “hypothesis paper,” and is thus more educated musing than real science, the paper marks the first time a respected, peer-reviewed scientific journal has been willing to put its name to such speculation.

As one of the journal’s editors points out, on the surface this seems to be just the latest in a long line of misleading conclusions arising from overzealous scouring of Curiosity‘s photos — but the incredibly detailed nature of these observations makes this paper uniquely hard to dismiss. Far from keying off of a single dune or a small pile of dirt, author Nora Noffke attempts to show that photos of one particular region of the Martian surface bear all the distinctive markings of an ancient, microbe-carpeted lakebed.

The region in question is the Gillespie Lake outcrop in Mars’ Yellowknife Bay, a dry ancient lake bed that underwent regular flooding, many billions of years ago. If there was any microbial life on Mars back then, theory says it probably acted roughly like Earth bacteria do in the same situation, and so the search for so-called microbially-induced sedimentary structures (MISS) has long been part of the astrobiological toolkit. Noffke’s argument then, that the MISS-like formations on Mars are probably actual MISS formations, is not totally out of left field — but if true, it is still revolutionary.

Microbially induced sedimentary structures occur when the floor of a shallow body of water, like a lake, becomes carpeted with microbial life. These layers of microbes trap and rearrange sediment, and eventually fossilize, creating recognizable layered structures over millions of years. What makes the photo comparison compelling in this case is there are multiple areas of overlap with Earthly MISS formations, from the banding of a chipped piece of stone to the imperfections in microbial coverage, to the implied order of ancient events. As you can see in the image below, Curiosity’s photo has been meticulously deconstructed, and Noffke’s past experience with MISSs on Earth makes her an authority on their identification.

Of course, this is just circumstantial evidence and could very easily be confirmation bias on the part of a scientist who’s spent years searching for signs just such as these. If nothing else, moon landing conspiracy theories ought to show how misleading it can be to take a photo and doodle all over it as though that means anything. If you’ve followed space science over the past decade, and in particular space life science, then the natural reaction is to dismiss these findings as shallow — but I mean, just look at these photos. All wishful thinking aside, and within the context of this paper‘s openly hypothetical status, it’s not irresponsible to get at least a little bit excited about these findings.

Of course, there are elements to this hypothesis that make it a bit difficult to believe, as well. Foremost among them, if microbial life existed on Mars in great enough quantities to have carpeted lake-beds and dictated large-scale rock formation, then why is there no other evidence of their existence? Curiosity has been blasting rock samples with lasers and measuring atmospheric methane to search for direct chemical evidence of current or ancient life, but so far the findings have been ambiguous at best. If microbes really did carpet Gillespie Lake for a long period, that might have been one of a small selection of places where that was the case.

Unfortunately, Curiosity has already rolled well past the site of these photos, and so it can’t scoop up any dirt for analysis. Noffke just recently found 3.5 billion-year-old MISSs in Australia, and you can bet those skills will be put towards spying and testing similar structures as the rover continues its journey across the Martian tundra.